Revamped I2C S-Meter for KD8CEC Firmware with Nextion. #arduino #fft #firmware #nextion #smeter

Dennis C (WC8C)

Here is something I want to share with the community. I have done quite a bit of work on the standalone S-Meter from KD8CEC.  The functionality Dr. Lee has provided in his firmware is fabulous, and this is my contribution to the effort.  I did this using a V4 board, but I think these changes are version independent - just requires use of KD8CEC firmware.

The Summary is below, full details are in the ReadMe on GitHub at  The new version is under i2cmeter2

This started with 2 simple goals in mind, but snowballed into a pretty large revamp and more improvements that I originally intended.  The original intent was:
  • Get the CW decode to function (it was not working for me)
  • Memory was very constrained - reduce memory usage so future new functionality can be added.
Here are some highlights. See the ReadMe on GitHub for the details.
  • CW decode mods - hard to tell degree of improvement, but it now works for me if the signal is not too weak.
  • Significant reduction in memory usage
  • More accurate frequency display on FFT (Requires a Nextion UI tweak)
  • Faster, higher resolution S-Meter (higher resolution Requires a Nextion UI tweak, High resolution is optional)
  • Calibratable S-Meter (and circuit for optional signal boost)
  • Calibratable Power/SWR Meter
  • Fixed several potential stability issues.  I never experienced instability - I corrected things I noticed that might have one day caused an issue.
  • Significant code streamlining and reorganization.
  • Optional faster Serial speed (requires tweak to Nextion and Ubitx firmware)
  • Improved frequency change latency when the FFT is being displayed
  • Optional support for using the Hardware serial output port instead of Software serial.
I also included my customized Nextion firmware (3.2" display)
  • Tweaks to go with the changes above.
  • Added Power and SWR meter screen (graphical)
  • Added Power and SWR (numeric) to main screen when transmitting - SWR flashes yellow/red when too high
  • Streamlined MEM to VFO screen
    • Frequencies are loaded when the screen opens
    • Selecting a frequency immediately returns to main screen
  • I think there may be other tweaks I did some time ago - I don't recall the specifics.

Dennis WC8C



Thank you.  It'll be a few days but I'm looking forward to trying this.



Thanks Dennis,
this looks really interesting, I think I’ll give it a try.

Mick VA3EPM 


Would love to have this for a Nextion 3.5

Dennis C (WC8C)

Give it a try.  It should work fine on 3.5.  It just won't use the whole screen.
Dennis WC8C